The object of this program is to investigate mechanisms of biological radiation damage, emphasizing factors at the molecular and cellular levels responsible for radiation sensitivity. Pulse radiolysis and steady irradiation studies are being carried out on micelles, enzymes, enzyme-drug complexes, bacteria and bacteriophage directed towards relating the initial damage at the molecular level to chemical and biological endpoints. The specific projects include: (a) Studies on the radiation sensitivity of E. coliphage emphasizing the effects of drugs that bind to DNA; (b) pulse radiolysis studies on micelles, as rudimentary membrane structures which may interact with and modify the radiosensitivity of biological target molecules; (c) pulse radiolysis and steady irradiation studies on drug-enzyme complexes; (d) investigation of potential carcinogenic hazards induced by drug- radiation interactions. The 40 MeV electron pulse radiolysis system available for this work has been linked to a PDP-11/45 digital computer, providing computer control of data acquisition and on-line data handling and analysis. Bibliographic references: "The oxidation of tryptophan by radical anions", J.L. Redpath, R. Santus, J. Ovadia and L. I. Grossweiner; Int. J. Radiat. Biol. 27, 201-204 (1975); "Role des ions 02 dans la formation de la N-formylcynurenine a partir du tryptophane"; P. Walrant, R. Santus, J.L. Redpath and D. Lexa; C.R. Acad. Sci. Paris 200, 1425-1428 (1975).